The present invention relates generally to the storage of radioactive chemical waste and metallic waste, and more particularly to an improved canister arrangement for jointly storing such waste.
The reprocessing of nuclear reactor fuel elements results in the formation of considerable quantities of high-level, long half-life radioactive waste in both chemical and metallic form. It is necessary to store this waste in such a manner that the radioactive material is prevented from contaminating the environment. The chemical waste has been previously encased in a vitreous matrix which is inert and exhibits relatively low solubility so as to contain the chemical waste in an environmentally safe manner. The glassified waste is usually cast in sealable steel canisters. The metallic waste on the other hand has been cast into a billet or solid cylinder form and encased in a suitable canister.
The storage of the chemical and metallic radioactive waste by techniques as described above does have some shortcomings. For example, while the glass matrix provides an excellent containment for high level chemical waste it possesses relatively low thermal conductivity values which do not allow for adequate dissipation of heat from the glass so as to yield deleteriously high temperature levels along the center line of the glass. Efforts to overcome such heating problems associated with the storage of radioactive material in glass include the incorporation of a heat-exchanging fin arrangement in the glass as described in assignee's U.S. Pat. No. 4,021,676 issued May 3, 1977. This fin arrangement provides an arrangement wherein center line hot spots in the glass cylinder are essentially eliminated.
Radioactive metallic waste is planned to be stored as a compact or as a billet in a canister separate from the glass-containing canister. The metallic waste storage poses some problems due to the canister volume and the material density. The metallic waste may be densified to near the theoretical density by melting the radioactive metallic waste into the form of a solid cylinder. However, unless such a solid cylinder can be produced of virtually the same diameter as the enveloping waste canister, the considerable advantages of casting billets to near theoretical density over compaction of the waste metal in the canister is substantially minimized. Further, hot cells capable of producing relatively long and large diameter cylinders of metallic waste are not presently available.
With high-level radioactive waste, strict administrative limits are set in such areas as canister size, maximum surface temperature, maximum glass temperature, maximum chemical waste (calcine) to glass frit composition ratio by weight, and maximum total canister heat content at the time of shipment.